Electrode for gaseous conduction devices



Jan. 5, 1937. s, us- 1 2,067,141

ELECTRODE FOR GASEOUS' CONDUCTION DEVICES Filed July 11, 1935 INVENTOR.

Patented Jan. 5, I937 PATENT OFFICE ELECTRODE FOR GASEOUS CONDUCTIONDEVICES Daniel S. Gustin, Bloomfield, N. J., assignor, by

mesne assignments,

to Westinghouse Electric and Manufacturing Company, East Pittsburgh, Pa,a corporation of Pennsylvania Application July 11, 1935, Serial No.30,778 8 Claims. (01. 176-126) My present invention relates to dischargedevices and has particular reference to an electrode therefor andconstitutes an improvement over the electrode shown and described in mycopending application Serial No. 757,658 filed December 15, 1934,assigned to the same assignee as the present invention.

Although an electrode constructed in accordance with my presentinvention may be utilized in various types of electrical devices it isparticularly adaptable to discharge lamps employmg metallic vapor as anionizable medium. In lamps of the metallic vapor type it is customary toemploy in addition to a small quantity of vaporizable metal, such asmercury, sodium, cadmium or the like, one or more rare gases forfacilitating starting of a discharge. During operation of these lampsthe vapor pressure thereof may be comparatively high but initially suchpressure is much lower and rises with the temperatures until thevaporizable metal is com pletely volatilized at which time maximumefficiency of the lamp is obtained.

To enable a rapid rise in temperature the tube is usually insulatedthermally by enclosing in an evacuated outer glass envelope which may beprovided with a gas filling to assist in heat insulating the inner tubeas well as the outer envelope forming a convenient structure for housingand supplying the electrodes of the tube with electrical energy.Moreover, with tubes of the high pressure metallic vapor type it isquite difiicult to initiate a discharge between the electrodes due tothe low pressure and temperature.

To overcome such disadvantage it has heretofore been the practice toemploy electrodes made of cores of alkaline earth compounds, such ascarbonates, hydroxides, or silicates with or without metal mixtures.Such cores are inserted in sections of highly refractory metal and theoxides activated by heating to a high temperature by the passage of anelectrical discharge or' in some instances by high frequency inductionheating.

Although electrodes constructed in such manner, when energized by thepassage of an electrical current, cause an initial discharge by reasonof the deposit of electron emissive material, which becomes emissiveeven at low temperatures and pressure, together with initial ionizationof the rare gases, nevertheless such electrodes are subject to certaininherent disadvantages. Since the electrodes are subjected to the hightemperature and ionic bombardment during operation of the tube aftervolatilization of the vaporizable metal the oxide surface vaporizes andsputters shortening the life of the tube and also causing a blackeningof the envelope.

It is accordingly an object of my present invention to provide animproved form of electrode r for a high pressure discharge device.

Another object of my present invention is the provision of an electrodeparticularly adaptable to high pressure discharge tubes wherein aportion of the electrode supplies a copious flow of electrons forinitially ionizing the gaseous medium within the tube and causing adischarge and upon a rise in temperature another portion of theelectrode receives the discharge during operation of the tube.

Another object of my present invention is the provision of an electrodeparticularly adaptable to high pressure discharge lamps employing ahighly refractory material wherein a portion of such metal is coatedwith a highly emissive electron material which supplies a copious flowof electrons at low temperature and pressure for initiating a dischargeand upon an increase in temperature and pressure the remaining portionof the electrode of refractory material assumes the discharge. 25

A further object of my present invention is the provision of anelectrode comprising a helix of refractory material having a furtherhelical winding of refractory material wound transversely to theconvolutions of the helix and 30 wherein a portion of the transverselywound helical windings are coated so as to be highly electron emissiveat low temperatures with the remaining portion being emissive at hightem- 35 peratures.

Still further objects of my present invention will become obvious tothose skilled in the art by reference to the accompanying drawingwherein: 40

Fig. 1 is a side elevational view 01' a discharge device including anelectrode constructed in accordance with my present invention,

Fig. 2 is an enlarged side elevational view 01 one of the electrodes asshown in the tube of 45 Fig. 1, and

Fig. 3 is an end view of the electrode taken on the line III-III andlooking in the direction of the arrows as shown in Fig. 2.

Referring now to the drawing in detail I have 50 shown in Fig. 1 a highpressure discharge tube comprising a discharge chamber 5 enclosed in anouter chamber 6 which latter may be evacuated and filled with a suitablegas to thermally insulate the chamber 5. Following my present inventionan electrode 1 is sealed-in at 8 and 9 to each end of the dischargechamber. This electrode comprises a wire I d of highly refractorymaterial, such as tungsten, which is wound into helical form of about 40turns per inch and, as shown more clearly in Fig. 2, may be ofapproximately six turns or convolutions in length. At about the centerof the helix the turns or convolutions are pulled out as shown at I2,while the remaining convolutions are left in close proximity to eachother. A helix of tungsten wire l3, having approximately 89 turns perinch, is slipped upon the remaining adjacent convolutions of thetungsten wire In at each end, which thus forms a core, so that the 0011-I volutions of the helix i3 are disposed transversely of those of thewire iii, and preferably adjacent convolutions are in contact with eachother to facilitate exhausting of the tube due to the electrode beingreadily heated by high frequency.

As shown there is a slight spaced relation between the coils of thehelix l3 providing interstices to receive a deposit of electron emissivematerial. Such a deposit of electron emissive material i4 is thenapplied to the helix l3 which is wound about the wire In adjacent to theenvelope wall through which the wire in extends while the opposite endcontaining the remaining helix i3 is left uncoated.

This coating can be applied by dipping the electrode into a suitablesolution of such material or the same may be sprayed thereupon and thusdeposited in the interstices and upon the coils l3. Such coating mayconsist of compounds of barium, strontium, etc., or other alkalicompounds which may be decomposed to oxides and activated by suitableheating, such as by high frequency induction treatment or the passage ofa discharge current after the electrodes are mounted within the lamp asis well known in the During operation of the lamp a suitable voltage isimpressed upon the oppositely disposed electrodes and due to the copiousflow of electrons from that portion of the electrodes having the coatingl4 they initially cause a resulting ionization of the gas with anaccompanying discharge despite the low temperature and pressure withinthe lamp. As the discharge continues the uncoated portion l3 of theelectrode becomes heated by the discharge to an electron emittingtemperature; which then assumes the discharge thus removing the samefrom the coated portion l4 and enabling the temperature and pressure ofthe lamp to increase and volatilize the vaporizable metal.

Moreover, the relatively large spacing provided by Pu ling out theconvolutions l2 prevents to a substantial extent the heat from theuncoated portion l3v being transmitted to the coated portion It, thusmaintaining the latter comparatively cool so as to inhibit appreciableelectron emission during normal operating temperature and pressure ofthe lamp. Also, despite the fact that vthe coated portion I l of theelectrode is maintained relatively cool, such has no effect upon thevapor pressure as there exists no pockets or dead space behind theelectrodes.

, In orde as before stated. to thermally insulate the lamp as well asform a convenient structure for housing the same it is disposed withinan outer envelope 6. This latter envelope is provided with a stem l5 atone end through which pass a pair of leading-in conductors l6 and I1sealed therein by a press IS in a well known manner. An exhaust tube i9is also provided for the purpose of evacuating the envelope 6 andintroducing a suitable gas, if desired, after which such tube is sealedoff. The leading-in conductor I6 is suitably joined to the wire Hi as bywelding 5 and similarly the conductor li extends longitudinally of thelamp 5 and may be secured to the wire it of the oppositely disposedelectrode in a like manner. A metallic winding 20 which is electricallyconnected to. the leading-in con- 10 ductor I! maybe employed to assistin supporting this conductor and also to facilitate starting of thelamp.

It can thus be readily seen by those skilled in the art that I haveprovidedan electrode par- 15 ticularly adaptable to discharge devices ofthe metallic vapor type wherein a portion of the electrode serves toinitiate a discharge at a low temperature and pressure after whichanother portion of the electrode assumes the discharge 20 upon thetemperature and pressure increasing during operation of the lamp.Inasmuch as that portion of the electrode which initiates the dischargeis maintained comparatively cool during normal operation of the lamp andalthough posi- 25 tioned in back of the normal operating portion of theelectrode the possibility of low pressure areas existing in the ends ofthelamp is eliminated by an absence of pockets or dead spaces. Moreoversuch a lamp after operation for pro- 30 longed periods of time is freefrom blackening and has a reasonable low starting voltage.

Although I have shown and described one specific embodiment of mypresent invention I do not desire to be limited thereto as various other35' modifications of the same may be made without departing from thespirit and scope of the appended claims.

What is claimed is:

1. An electric discharge device provided with 40 convolutions of saidfirst mentioned helical winding, and a coating of high electron emissivematerial disposed upon a portion of said transverse- 0 1y wound helicalwinding positioned fartherest from the oppositely disposed electrode. 2.An electric discharge device provided with a sealed envelope and havingan operating electrode extending into and sealed through the wall 55 ofsaid envelope, said electrode comprising a helix with approximately thecenter convolutions thereof extended to provide a relatively largespacing between the remaining convolutions at each end of said helix, ahelical winding dis- 50 posed transversely of the relatively closelypositioned end convolutions of said helix, and a coating of electronemissive material disposed upon said transversely wound helical windingat the end of said helix in closest proximity to the o5 portion of saidenvelope to which said electrode is sealed.

3. An electric discharge device provided with a gaseous fillingincluding a metal vapor and operating with a high pressure dischargecom- 70 prising a sealed envelope, an operating electrode of refractorymaterial extending into and sealed through the wall of said envelope ateach end thereof and wound into a helix. interiorly of said envelope andcoaxially disposed relative to the longitudinal axis of said envelope, ahelical winding of refractory material transversely disposed relative tothe convolutions of said helix and having a portion thereof disposedfartherest from the oppositely disposed electrode coated-with anelectron emissive material for the purpose of ionizing the gaseousfilling and initiating a discharge between said electrodes uponenergization thereof in order to heat the remaining uncoated portion ofsaid electrodes to an electron emitting temperature and cause thedischarge to be concentrated between the latter upon an increase intemperature and pressure of said device.

4. An electric discharge device provided with a gaseous fillingincluding a metal vapor and operating with a high pressure dischargecomprising a sealed envelope, an electrode of refractory materialextending into and sealed through the wall of said envelope at each endthereof and wound into a helix with approximately the center convolutionthereof extended to provide a relatively large spacing between theremaining convolutions at each end of said helix and to substantiallyprevent the transmission of thermal energy between the spiral ends ofsaid helix during operation of said device, said electrodes including ahelical winding of refractory material disposed transversely of therelatively closely positioned end convolutions of said helix and havinga coating of electron emissive material disposed upon said transverselywound helical winding fartherest from the opposite electrode for thepurpose of ionizing the gaseous filling and initiating a dischargebetween said electrodes upon energization thereof in order to heat theremaining uncoated portion of said electrodes to an electron emittingtemperature and cause the discharge to be shifted between the latterupon an increase of temperature and pressure of said device.

5. An electrode for a discharge device comprising a helically wound wireof refractory material having approximately the center convolutionthereof extended to provide a relatively large spacing between theremaining end convolutions of said wire, a helical winding of refractorymaterial disposed upon the relatively closely spaced end convolutions ofsaid wire and positioned transversely of the latter, and a coating ofelectron emissive material disposed upon a portion of said transverselywound helical winding.

6. An electrode for a discharge device comprising a section providedwith an activated coating, a section consisting of a base metal, and aheat dissipating section intermediate said first two mentioned sections.

7. An electrode for a discharge device comprising a section of helicalform provided with an activated coating, a section consisting of a basemetal of helical form, and an intermediate heat dissipating sectionbetween said aforementioned sections.

8. An electrode for a discharge device comprising a refractory metalcore of helical form, a section of said core being provided with ahelical winding having an activated coating, 9. further section having ahelical winding of a base metal, and an intermediate section comprisingsaid core and having the convolutions thereof extended to provide a heatdissipating section between said sections having the helical windings.

DANIEL S. GUSTIN.

